Significant Accounting Policies (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Significant Accounting Policies
Utility plant acquisition adjustments	$ 2,904	$ 2,658
Amortization of utility plant acquisition adjustments	50	50	50
Deferred investment tax credits	812	851
PPUC approved rate for AFUDC (in hundredths)	0.1004	0.1004	0.1004
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Total Utility Plant	292,483	281,002
Effective rate of depreciation (in hundredths)	2.13%	2.11%	2.06%
Regulatory Assets and Liabilities [Abstract]
Regulatory assets	23,835	23,114
Interest Rate Swap Derivatives [Abstract]
Interest rate swap settlements reclassified to interest expense	362
Interest rate swap gain (loss) capitalized	358
Interest rate swap settlements to be reclassified during the next 12 months	357
Interest rate swap expire period	Oct. 01, 2029
Income taxes [Member]
Regulatory Assets and Liabilities [Abstract]
Regulatory assets	5,459	5,174
Regulatory liability	836	875
Postretirement benefits [Member]
Regulatory Assets and Liabilities [Abstract]
Regulatory assets	14,244	13,949
Unrealized swap losses [Member]
Regulatory Assets and Liabilities [Abstract]
Regulatory assets	2,807	2,811
Utility plant retirement costs [Member]
Regulatory Assets and Liabilities [Abstract]
Regulatory assets	1,313	1,098
Remaining Recovery Periods, Assets	5 years
Rate case filing expenses [Member]
Regulatory Assets and Liabilities [Abstract]
Regulatory assets	2	82
Remaining Recovery Periods, Assets	2 years
Service life study expenses [Member]
Regulatory Assets and Liabilities [Abstract]
Regulatory assets	10	0
Remaining Recovery Periods, Assets	5 years
Minimum [Member] | Income taxes [Member]
Regulatory Assets and Liabilities [Abstract]
Remaining Recovery Periods, Liability	1 year
Minimum [Member] | Postretirement benefits [Member]
Regulatory Assets and Liabilities [Abstract]
Remaining Recovery Periods, Assets	10 years
Minimum [Member] | Unrealized swap losses [Member]
Regulatory Assets and Liabilities [Abstract]
Remaining Recovery Periods, Assets	1 year
Maximum [Member] | Income taxes [Member]
Regulatory Assets and Liabilities [Abstract]
Remaining Recovery Periods, Liability	50 years
Maximum [Member] | Postretirement benefits [Member]
Regulatory Assets and Liabilities [Abstract]
Remaining Recovery Periods, Assets	20 years
Maximum [Member] | Unrealized swap losses [Member]
Regulatory Assets and Liabilities [Abstract]
Remaining Recovery Periods, Assets	17 years
Mains and Accessories [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Total Utility Plant	152,193	146,290
Mains and Accessories [Member] | Minimum [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Approximate range of remaining lives	8 years
Mains and Accessories [Member] | Maximum [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Approximate range of remaining lives	84 years
Services, meters and hydrants [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Total Utility Plant	59,211	56,731
Services, meters and hydrants [Member] | Minimum [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Approximate range of remaining lives	19 years
Services, meters and hydrants [Member] | Maximum [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Approximate range of remaining lives	55 years
Operations structures, reservoirs and water tanks [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Total Utility Plant	42,186	41,435
Operations structures, reservoirs and water tanks [Member] | Minimum [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Approximate range of remaining lives	15 years
Operations structures, reservoirs and water tanks [Member] | Maximum [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Approximate range of remaining lives	43 years
Pumping and treatment equipment [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Total Utility Plant	22,933	21,585
Pumping and treatment equipment [Member] | Minimum [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Approximate range of remaining lives	4 years
Pumping and treatment equipment [Member] | Maximum [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Approximate range of remaining lives	32 years
Office, transportation and operating equipment [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Total Utility Plant	10,728	9,786
Office, transportation and operating equipment [Member] | Minimum [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Approximate range of remaining lives	2 years
Office, transportation and operating equipment [Member] | Maximum [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Approximate range of remaining lives	22 years
Land and other non-depreciable assets [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Total Utility Plant	3,121	2,980
Approximate range of remaining lives	0 years
Utility plant in service [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Total Utility Plant	290,372	278,807
Construction work in progress [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Total Utility Plant	$ 2,111	$ 2,195
Approximate range of remaining lives	0 years